1. Technical Field
The present disclosure relates to a power amplifier circuit.
2. Description of the Related Art
Recently, there has been an increasing shortage in radio frequency due to the increased use of radio technology such as radio communications and radar. One solution to relieve the shortage of frequency is to use a millimeter waveband, for example. Use of a millimeter waveband has already been implemented in some radio apparatuses. For example, the 60 GHz band is used in millimeter wave communication and the 79 GHz band is used in millimeter wave radar. With this background, a frequency band over 100 GHz, which is a higher frequency than the above frequencies, is expected to be utilized. A radio apparatus using a frequency band over 100 GHz is capable of occupying a broader band than conventional radio apparatus using a lower millimeter waveband. A radio apparatus using a frequency band over 100 GHz has accordingly been receiving attention from the viewpoint of the capability of implementing higher-speed communications and higher-resolution radar. Hence, use of radio ICs operating at over 100 GHz is widely anticipated.
The following issue arises in the development of radio ICs capable of operating at over 100 GHz. Specifically, a power amplifier circuit, which is a component of a radio IC, uses a passive component such as an inductor in its input or output circuit, for example. Performance of the inductor is represented by an index, the Q factor. The power amplifier requires an inductor with a high Q factor for gain enhancement. A configuration disclosed in “Q-enhanced 1.9 GHz tuned CMOS RF amplifier” IET Electronics Letters, VOL. 32, Issue: 5, February 1996 is widely known as a configuration for enhancing the Q factor.